1. Field of the Invention
The invention relates to a self-balancing vehicle equipped with:
at least three wheels, of which at least two wheels are situated on either side of the centre of gravity of the vehicle's longitudinal axis and wherein at least one of the wheels has a steering effect on the direction of the vehicle,
a frame consisting of a tilting frame section, wherein said frame section can rotate in the longitudinal axis relative to the road surface,
a steering means which is mounted so that it can rotate relative to the tilting frame section,
and one or more tilting elements which form a connection between the tilting frame section and the wheels in such a way that said tilting element can exert a tilting moment and/or tilting movement between the tilting frame section and the road surface. What can be achieved by this is that the vehicle is in a completely or partially balanced state during use.
2. Description of the Related Art
A known vehicle of the type referred to above is described in WO 95/34459 in the name of the applicant. This vehicle is a self-stabilising vehicle with at least three wheels, wherein a sensor connected to the direction-determining wheel generates a control signal to control one or more tilting elements. With this arrangement the force or moment acting on the front wheel is measured with the aid of a sensor and the driver's section is tilted by means of hydraulic cylinders in such a way that the force or moment exerted on the front wheel becomes practically 0. This results in a stable and comfortable driving behaviour and the driver's section remains balanced in bends or when driving on laterally sloping surfaces. This vehicle operates particularly well at speeds above 10 km/h and will exhibit an undesirable tilting behaviour at very low speeds, when stationary, during parking manoeuvres and reversing.
Another known vehicle of the type referred to above is described in WO 99/24308 in the name of the applicant. This vehicle is a self-stabilising vehicle with at least three wheels, wherein an opposite lock power transmitter is connected to a steerable front wheel. As a result, the vehicle operates even better at high speeds. However, this invention does not provide any solution for balancing at low speeds, when stationary, or during reversing.
Another known vehicle of the type referred to above is described in WO 99/14099 in the name of the applicant. This vehicle is a self-stabilising vehicle with at least three wheels, wherein a sensor determines the turning angle between the front wheel and the steering column and controls one or more tilting elements of the vehicle, depending on the turning angle. This vehicle is also equipped with a system that puts the vehicle in a perpendicular position relative to the road surface at low speeds and when stationary. However, this solution at low speeds does not work as required on a laterally sloping surface. The vehicle is then out of balance and on changes in speed will vary between a balanced state at high speeds and a perpendicular state at low speeds or when reversing.
Another known vehicle analogous to the type referred to above is described in EP0 941 198.
This vehicle is a self-stabilising vehicle with three wheels, a tilting vehicle section and a non-tilting vehicle section and employs a sensor that measures the vehicle speed, a sensor that determines the lateral acceleration and a sensor that determines the tilt angle of the non-tilting vehicle section relative to the centre of gravity. Below a certain speed, typically 3 km/h, these last two sensors generate the required control signals for the microprocessor control system which then controls the one or more tilting elements via a hydraulic circuit. Above this transitional speed, the hydraulic circuit is left open, as a result of which no forces are exerted from the one of more tilting elements. As a result of this, the vehicle assumes a driving and steering behaviour at higher speeds analogous to that of a motorcycle consisting of two wheels. Consequently this vehicle is difficult to steer because the transition from low speed to high speed is difficult for the driver to learn. In addition, the system offers no solution for coping with a large imbalance at high speed. It is also not suitable for vehicles with four wheels.
Vehicles that are equipped with a lateral acceleration sensor have the major disadvantage that they have a late reaction speed to changes in direction. Moreover, such lateral acceleration sensors react sharply to transient lateral accelerations that are typical at high speeds. These sensors also react sharply to lateral accelerations that are caused by the tilting movements of the vehicle. As a result of this, tilting systems equipped only with a lateral acceleration sensor exhibit a nervous and oscillating behaviour, particularly at high speeds. For this reason, various extremely complicated measurement and control systems are often used to attenuate this oscillating behaviour. This often leads to even later reaction speeds, as a result of which the stability of the vehicle is at risk.
Vehicles equipped with a steering sensor do not exhibit these disadvantages, but do not operate totally satisfactorily at low speed and particularly when stationary. Force moments on the steering wheel, which are often the case at low speeds (under 10 km/h), often result in a tilting that does not contribute to the desired balance situation. As a result of this, tilting systems equipped with only a steering sensor exhibit exaggerated and undesirable tilting movements which are experienced by the driver as undesirable. For this reason, a system is described in WO 99/14099 in the name of the applicant wherein below a given speed the tilting behaviour is switched off and the vehicle is positioned upright. The relatively small disadvantage of this system is the fact that a transition then takes place between a balanced state and an unbalanced state. Particularly on sloping road surfaces, this is experienced as undesirable.